I’ve had quite a few annoying paint blisters on my Jazz bass build. You can’t get the finish too hot before it’s had a chance to dry otherwise the surface goes hard whilst you’ve still got solvent underneath. This vaporises and the gas forms those bubbles. If you ate quick, you can pop it and push the bubble down so it sticks back again with minimal damage. But certainly with nitro, the solvent softens the layers below, and left too late, the bubble can take off more paint with it, leaving a pit below it which takes more filling.

You have my sympathy.